The known needled multilayered carpets have a backing of film or woven tape. An intermediate layer of fibers is arranged on this backing, which is covered by a top layer of carpet made of better fibers that are visible in use. These three layers are needle-punched together, and fibers from the top layer are needle-punched into the intermediate layer and the backing.
The bottom or intermediate layer make the carpet thicker, for one thing, and for another, the intermediate layer is used to achieve a better hold for the fibers needled through from the top layer of the carpet. As a rule, this intermediate layer is 2-3 mm thick. Although cheaper fibers are used for the intermediate layer, substantial costs are involved in processing these fibers.
After being needled, the fibers in the intermediate layer are tightly integrated by impregnating the carpet with a binder, like latex, or at least slop-padded from beneath up to the upper edge of the intermediate layer. This way, the fibers in the top layer of the carpet are reinforced and anchored fast, so they cannot be pulled out as the carpet is used. The process of drying a carpet produced in this process is expensive in terms of time and energy. Large machinery is required, and the process must be closely supervised. Integrating the latex into the carpet and cross-linking it represents a large and hence onerous production expense, and special drainage and ventilation problems occur. These carpets also have the disadvantage that old carpets are very difficult to dispose of, since the latex components are very difficult to separate from the other components in the carpet, and the ratio of elastomers to total raw materials is bound to be non-uniform, for the most part.
Many attempts have been made to improve or optimize the properties of needled-felt carpets. Thus, it is known from AT 305 942, how to put a thermoplastic film between the top and bottom layer, which is bonded to the top and bottom layer by needling, and then surround it with a foamed PVC paste in such a way that the film disappears in it.
The use of polyethylene films processed with needled felt is known from DEZ Chemiefaser 2/69, pp. 103-106. These films are used in order to improve the expansion properties of the carpets produced with them.
In the carpet known from DE OS 22 19817, strips of polypropylene are used as woven tape.
But none of the carpets disclosed in the documents named eliminate the disadvantages mentioned at the beginning of complicated, expensive and environmentally harmful production processes.